The objective of this investigation is to analyze specific developmental events and their temporal and spatial coordination. We will study morphological changes in the earliest phases of a Drosophila embryo. We will determine the elements of the cytoskeleton which move the nuclei to specific positions at specific times. These earliest phases of development are maternally regulated and at a specific stage, the zygotic genomic activity regulates the continuation of embryogenesis. We have begun to study how the transformation from maternal to zygotic control occurs and have pre observations which indicates that the normal program of development is regulated by multiple and synchronized time measuring devices. We will identify these mechanisms and ultimately hope to characterize genes and their products which regulate these mechanisms. Upon activation of transcription the embryo gastrulates and after gastrulation movements the three germlayers, ectoderm, mesoderm and endoderm, are established. As a consequence of these movements, cells have new neighbors. We will determine whether interactions with these new neighbors are required for the differentiation of germlayer specific identities.